In the field of power plant facilities, it is important to analyze the plant thermohydraulic properties or phenomena for maintaining the facility and training operators to perform routine and emergency monitoring and procedures. It is known to analyze power plant thermohydraulic phenomena using engineering codes such as the well known RELAP5/MOD3, and to conduct real time simulations for operator training of power plant two phase thermohydraulic phenomena with engineering code methodologies.
RELAP5/MOD3 is an engineering code that can provide analysis of steady state and transient thermohydraulic conditions. It applies field equations (also known as balance or conservation equations), state equations, closure correlation flow regime maps and a two-step semi or nearly implicit numerical scheme for solving the thermohydraulic properties, e.g., pressure and momentum (or velocity). One deficiency in applying RELAP5/MOD3 in the real time domain is that it uses variable time steps to assure system stability during severe transient calculation. However, this approach will not guarantee that it can run in real time under all operating conditions. Another deficiency with RELAP5/MOD3 is that it cannot be used to simulate a complete cycle of power plant performance from start up to shut down continuously. Consequently, the code is limited in its application to engineering analysis.
In view of the risks posed by power plant accidents, there is a continuing need for improved methods and devices for simulating in real time a wide variety of power plant thermohydraulic phenomena with high fidelity. A high fidelity simulator is one that can satisfies the simulator testing standard (e.g., ANSI/ANS 3.5 1991 in U.S.A.), which requires more rigorous validation and performance testing than the prior standard, and also enables operators and safety engineers to better understand the physical mechanisms of plant performance, thereby preparing them to face events and phenomena which were not previously encountered. It is desirable that such a high fidelity simulator bear the safety analysis code grade best-estimate capability in accordance with existing industry and regulatory organization requirements.
Existing simulators typically rely on either the two-fluid (6 equations) or the mixture models (3 or 4 equations) see, e.g., Fabic, "On Choices Between The Two-fluid And The Mixture Models For Simulation Of Severe Transients In Nuclear Power Plants," Key Note Speech on the Simulation Multiconference on Simulators International VIII, 1-5 Apr. 1991; Ishii, "Foundation of Various Two phase Flow Models and their Limitations," Argonne National Laboratory; Ishii, "Two-Fluid Model for Two phase Flow," Chapter 1, Multiphase Science and Technology, Volume 5, 1990; Wulff, "Computational Methods for Multiphase Flow," Chapter 3, Multiphase Science and Technology, Volume 5, 1990; and Agee, "Capabilities and Limitations of LWR System Analysis Codes," RELAP User Seminar, College Station, Tex., 1989. The mixture models use one set of mass, energy and momentum equations (i.e., 3 equations) to describe the behavior of mixture phase. Individual phasic phenomena are simulated by correlation models, such as drift flux model. The two-fluid model considers each phase separately in terms of two sets of mass, energy and momentum equations (i.e., 6). Closure correlations for interfacial relationships and wall-fluid interactions are required.
Other analysis techniques using 4 or 5 equations are also known. Such models can be viewed as advanced mixture models and their complexities lie between mixture and two-fluid models. The two-fluid model is regarded as mathematically more complete and rigorous than the mixture model. However, it requires much more physical understanding of the interfacial transfer laws as well as more sophisticated numerical methods to obtain optimal performance.
Thermal hydraulic models (especially for real time simulators) are also discussed in terms of nodal or loop momentum methods and nodal or system pressure methods. See, e.g., Fabic, "On Choices Between The Two-fluid And The Mixture Models For Simulation Of Severe Transients In Nuclear Power Plants," Key Note Speech on the Simulation Multiconference on Simulators International VIII, 1-5 Apr. 1991; Wulff, "Computational Methods for Multiphase Flow," Chapter 3, Multiphase Science and Technology, Volume 5, 1990; and Fabic, "Thermal Hydraulics in Nuclear Power Plant Simulators," Proceedings of the Third International Topical Meeting On Reactor Thermal Hydraulics, Newport, R.I., 1985. The Nodal Momentum Nodal Pressure (NMNP) method considers conservation of momentum, mass and energy for each node. Examples of this method includes known safety analysis engineering codes like RECAP, TRAC, RETRAN, ATHLET, and CATHARE and real time simulation codes like SIMARC, CETRAN and TRACS.
The Loop Momentum System Pressure (LMSP) method considers momentum balance for a closed loop (not for a node) and fluid properties are calculated based on a system pressure. Many problems encountered with this method are well known. Fluid properties based on a system pressure fails to simulate conditions where hydraulic pressure is an important factor in the total pressure calculation. Fluid cells not in a loop require decoupled treatments, thus it loses fidelity of prediction. It also fails to simulate conditions where a loop is broken by isolation valves. Interfacial heat balance and mass balance are numerically calculated in two successive time steps, and thus are not consistent. This causes numerical instabilities in fast transients calculation. Examples of this method include the engineering code RAMONA and real time code RETACT.
The advances in RISC-based workstation technology, and its equivalents, and developments in engineering code principles have stimulated the need for improved real time analysis methods suitable for both engineering analysis and simulation for operator training. It is known that efforts have been made to install the TRAC engineering analysis code on a CRAY super-computer for real time simulation. However, the expense of purchasing and maintaining such a super computer is expected to render such a combination impractical for commercialization. It also has been reported that use of the RELAP code in real time was under study.
It is therefore, an object of the present invention to provide an integrated methodology for real time analysis of power plant thermohydraulic phenomena. It is another object to provide real time analysis of power plant thermohydraulic phenomena that can be used for simulation training of facility operators and for engineering analysis of such phenomena, separately or simultaneously.
It is another object of the invention to provide a real time analysis of power plant thermohydraulic phenomena under normal and emergency operating conditions.
It is another object of the invention to simulate real time power plant thermohydraulic phenomena under normal, emergency, and beyond design conditions.
It is another object of the invention to provide an improved analysis of two phase flow in a power plant hydraulic system.
It is another object of the invention to provide an improved analysis of thermal transfer in a fluid flow system.